Quantum dots of CdS with hexagonal phase were prepared at relatively low temperature (60 oC) and short time by micro-emulsion (O/W) under ultrasound. This study was focused on the particle size distribution and the growth kinetics. The particle size distribution obtained from the optical absorption edge. It was relatively symmetrical with sonication time. In addition, an agreement was observed with the size distribution obtained from the TEM images of the sample under ultrasound. The growth kinetics was monitored by the red-shift in UV-Visible absorbance peaks. The cubed average particle radius showed an emergence of linear regions at longer times. This indicates that the increase of particle size at longer time can be attributed to the diffusion-limited coarsening process. The rate constant for the coarsening increases with increasing the temperature. The Arrhenius-type plot was created by using the slopes of Lifshitz-Slyozov-Wagner (LSW) curves. The activation energy was 71.72 kJ.mol-1 for the ripening process. In fact, the acoustic cavitation strongly increases the diffusion of surface atoms.